<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>outline</title>
    <style>
        .out {
            /* width: 100px; */
            height: 60px;
            /* width: calc(100px-40px); 报错 + - 旁边要加空格 
            参考：https://juejin.cn/post/7055169229980434462*/
            width: calc(100px - 40px);
            margin: 25px;
            background: yellowgreen;
            border-radius: .4em;
            border: 5px solid #655;
            outline: 5px solid deeppink;
        }
    </style>
</head>

<body>
    <div class="out"></div>
</body>

</html>